Ok,
I've been driving my car around all day today and everything seemed fine. Tonight, I left my parents house (who live about a mile from me) and as I was pulling into my neighborhood, the car stuttered and the CEL started flashing. I figured it was a bad coil pack and no big deal. I did notice the CEL flahsed for a couple seconds about 2 weeks ago when I started the car once but it stopped. A little while after that, my alternator went bad and burnt up -so I replaced it and I figured that was the issue until it started again tonight. I drove about a half mile home and broke out the VAG-COM.

When I got out of my car, the rotten egg smell was pretty strong. I have the worst sense of smell, so if I could smell it then it must have been bad.

My VAG-COM pulled a bunch of misfire codes - 0300, 0302, 0303, 0305 and 0306. The only other code was 1602 - Power Supply B+ Terminal 30: Voltage too Low . I am guessing the 1602 is due to the failed alternator that I replaced - I will clear the codes and see if it comes back, as I would have thought it would have cleared itself after almost 2 weeks.

I know that any number of things could be causing such a misfire, and without any other codes (such as o2 sensors, cats, etc) it can be difficult to diagnost. Any suggestions are welcome...

My bigger question is this - does the rotten egg smell definitively mean that one or both cats are bad? Or is it realistic that the serious misfire situation created the smell and would have damaged the cats if driven for any length of time?

As always, thanks for the help...

Oh, btw - this is a 2004 A6 2.7TQ

 

Your battery will also emit a sulphur smell when it is dry and practically dead. Since that is what happened with me and after a new battery I was good to go. As for the misfire codes... Well I wish you I could provide more insight.

 

roten eggs ? your boiling your battery ...
your alternator or regulator is kicking out WAY to much voltage ..

 

Typically rotten eggs is sulfur, and comes from the cats. Does it mean they are dead? I dont think so. It may well mean it is running rich -- anything that causes incomplete burn.

This could be cats, 02 sensors, heaters, overall mixture S[n]NAFU....

G

 

The battery thing is an interesting avenue - I will check the voltage tonight. It's a newer battery and the voltage meter has been spot on, so I am not sure this is it, but it's worth a look to make sure there's no thermal run-off.

I checked the passenger O2 sensors last night and they were both at about 8.5-8.8 ohms on pins 1-2, so that looks good. I could not for the life of me get to the two driver's side O2 sensor connections. I removed the coolant resevoir, and I can see the connectors if I look REALLY carefully through some wires, but there's this one harness that goes over them and I can't seem to move it enough to get access to the sensor connections - I will take another look tonight. I also came across a vag-com test in the bentley that I will examine further to check the O2s.

I may just get 6 new plugs and pop them in also this week - it's prolly due for a tune-up. I've put about 50,000 on the car myself and I think it was tuned up before I bought it ...but who knows for certain?

I also plan on checking the MAF and coil packs with parts from my mom's 01 A6 2.7T.

Also, I moved the car in my driveway this morning to get it out of the way of my other car. No sulfur smell, no CEL, no flashing CEL. It did run rough though and I could feel it misfire even under very light throttle. It seems the smell and CEL may have been caused by the car warming up perhaps....

Thanks for the input guys!

 

Another update. I had some more time tonight to look at this with the Vag-Com. I cleared all the codes and idled the car. When doing this, there's no rotten egg smell, and ever 10-15 seconds the engine stutters and car shakes.

I kept checking for codes and none were being thrown. I checked the measuring blocks in the engine module on the Vag-com and found that cylinder 6 misfires whenever the car shakes. #6 misfired 8 times and none of the others had a single misfire. My theory at this point is that it's a simple coil pack issue, but it's misfiring so badly that it's throwing the timing off on the other cylinders when under throttle.

I am going to grab a new coil pack and replace it tomorrow (it's way too cold out tonight and I don't have a spare). Now, I am looking for a diagram that shows which cylinder is #6. I am sure I'll find it from searching, but if anyone knows, I'd appreciate it.

Thanks again to all those that chimed in.

 

You can do that or simply switch #5 with #6. If misfire moves to #5 then you replace #5 (the now-bad) coil.

You should look at the plug in #6 anyway...it's possible if unlikely the plug is damaged.

Of course, if you have a spare coil, knock yourself out.

 

Cylinder #6 is on the driver's side at the rear. The firing order is 1,4,3,6,2,5. The cylinders are numbered 1,2,3 on the passenger side with 1 being in front and 4,5,6 are on the driver's side with 4 being on the front.

 

Sorry for not updating this sooner guys - but as soon as I got this fixed I got side-tracked into other things.

It was cylinder #6. I pulled it and took a coil out of my gf's A4 and everything ran smoothly. So I went to Audi and dropped $23 on a new one, which was better than the $35 I thought they'd charge.

Amazing how one bad coil can cause misfires on almost all cylinders. It's also amazing how the vag-com allowed me to watch each cylinder to see the misfires...right there probably saved me $80-160 in diagnosis fees.

Thanks for all the help. I was worried about nothing!